How to test mail server using telnet

Telnet is a great tool to test a mail server's functionality. Here's a step-by-step guide on how to use telnet to test a mail server:

Prerequisites:

You have a mail server set up and running.
You have telnet installed on your system (it's usually pre-installed on most operating systems).
You have a basic understanding of SMTP (Simple Mail Transfer Protocol) and email protocols.

Testing the Mail Server using Telnet:

Open a telnet session: Open a command prompt or terminal and type telnet followed by the mail server's hostname or IP address. For example:
```
telnet mail.example.com 25
```
Replace mail.example.com with your mail server's hostname or IP address, and 25 with the SMTP port (which is usually 25).
Establish a connection: Press Enter to establish a connection to the mail server. You should see a response like this:
```
Trying 192.0.2.1...
Connected to mail.example.com.
Escape character is '^]'.
```
Replace 192.0.2.1 with the IP address of your mail server.
Send a HELO command: Type HELO followed by a space and your client's hostname (e.g., your computer's hostname). Press Enter:
```
HELO myclient
```
The mail server should respond with a greeting message, like this:
```
250-mail.example.com Hello myclient [192.0.2.100]
```
Send a MAIL FROM command: Type MAIL FROM followed by a space and the email address you want to send from (e.g., [email protected]). Press Enter:
```
MAIL FROM: [email protected]
```
The mail server should respond with a message indicating that the email address is valid, like this:
```
250 2.1.0 Address accepted
```
Send a RCPT TO command: Type RCPT TO followed by a space and the email address you want to send to (e.g., [email protected]). Press Enter:
```
RCPT TO: [email protected]
```
The mail server should respond with a message indicating that the email address is valid, like this:
```
250 2.1.5 Recipient accepted
```
Send a DATA command: Type DATA followed by a space. Press Enter:
```
DATA
```
The mail server should respond with a message indicating that it's ready to receive the email message, like this:
```
354 Start mail input; end with <CRLF>.<CRLF>
```
Send the email message: Type the email message you want to send, followed by a blank line to indicate the end of the message. Press Enter:
```
Subject: Test email from telnet
```

This is a test email sent from telnet.

8. **Send a QUIT command**: Type `QUIT` followed by a space. Press Enter:

QUIT

The mail server should respond with a message indicating that the connection is closed, like this:

221 2.0.0 Bye


**Troubleshooting:**

If you encounter any issues during the test, you can try the following:

* Check the mail server's logs for errors.
* Verify that the mail server is configured correctly.
* Check the DNS records for the mail server to ensure that they are correct.
* Try using a different telnet client or a different method to test the mail server.

By following these steps, you should be able to test your mail server using telnet and ensure that it's functioning correctly.

Mail Knowledge

How to test mail server using telnet